WASHINGTON -- Senators compromised Thursday on a bill that attempts to spell out the military's right to detain Americans indefinitely, killing a bid to bar the practice but passing an amendment that says current laws on the matter stand.

The provision in the National Defense Authorization Act aimed to codify a string of court cases and current anti-terrorism practices involved in the capture and treatment of terrorism suspects. It initially opened what opponents saw as the prospect of letting the military haul away any citizen about whom it had suspicions.

The new amendment specifies that the current practices may not change, although it also says explicitly that the military can pursue Americans at home.

"Nothing in this section shall be construed to affect existing law or authorities relating to the detention of United States citizens, lawful resident aliens of the United States or any other persons who are captured or arrested in the United States," says the compromise amendment, which passed 99 to 1.

Update Dec. 3, 9 a.m.
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Sen. Jon Kyl (R-Ariz.) was the lone opponent.

The passage may head off a showdown with the White House, which had threatened to veto the entire bill on the grounds that the section on detentions tied the hands of counterterrorism officials in law enforcement and the military.

The White House did not immediately weigh in on the new measure.

Left unresolved by the new language is just exactly what is constitutional when it comes to detaining American citizens in the United States. But opponents of the original provision said at least it would remain up to judges, not politicians.

"To this day the Supreme Court has never ruled on whether it is constitutional to indefinitely detain a U.S. citizen captured in the United States. Some of my colleagues see this differently, [but] the language we've agreed on makes it clear," said Sen. Dick Durbin (D-Ill.), who had been adamantly opposed to giving the military what he saw as greater reign over Americans at home.

"The Supreme Court will decide who can be detained; the United States Senate will not," Durbin said.

The deal was cut by Sens. Lindsey Graham (R-S.C.) and Dianne Feinstein (D-Calif.), among others, but Feinstein still insisted on a vote for her own amendment that would have explicitly barred the military from detaining U.S. citizens without hearings or a trial. It failed 45 to 55.

Senators who favor giving the military explicit power in the U.S. said the new amendment allows the country to use whatever means it needs to to keep America safe.

"The threats we face as a nation are growing. Homegrown terrorism is going to become a greater reality, and we need to have tools," Graham argued. "Law enforcement is one tool, but in some cases holding people who have decided to help al Qaeda and turn on the rest of us and try to kill us so we can hold them long enough to interrogate them to find out what they're up to makes sense."

"When you hold somebody under the criminal justice system you have to read them their rights right off the bat," Graham added. "Under the law of war you don't because the purpose is to gather intelligence. We need that tool now as much as any time, including World War II."

Earlier, Feinstein made an impassioned plea for preserving American freedoms.

"This constant push that everything has to be militarized .... I don't think that creates a good country," Feinstein argued. "Because we have values. And due process of law is one of those values. And so I object, I object to holding American citizens without trial. I do not believe that makes us more safe."

The overall Defense bill passed Thursday night 93-7, but it will now have to be meshed with a differing version in the House. As part of the detention compromise, Feinstein extracted a promise from Senate leaders that they would insist on the Senate's new language remaining in the final product. It could change, however.

The American Civil Liberties Union found the compromise troubling, and said the president should still veto the bill because even with the no-change language, the measure sets in stone the military's ability to operate inside the U.S. borders.

"The bill is an historic threat to American citizens and others because it expands and makes permanent the authority of the president to order the military to imprison without charge or trial American citizens," said ACLU senior legislative counsel Christopher Anders in a statement.

"The final amendment to preserve current detention restrictions could turn out to be meaningless and Sens. [Carl] Levin [Michigan Democrat] and Graham made clear that they believe this power to use the military against American citizens will not be affected by the new language," Anders said. "This bill puts military detention authority on steroids and makes it permanent. If it becomes law, American citizens and others are at real risk of being locked away by the military without charge or trial."

Michael McAuliff covers Congress and politics for The Huffington Post. Talk to him on Facebook.